The present invention relates to a low temperature flexible, water-repellant polysiloxane containing copolymer particles dispersed therein. More specifically, the present invention relates to the copolymer particles being formed in situ by polymerizing at least two different types of monomers in the polysiloxane which is curable at low temperatures; for example, an ambient temperature, upon exposure to moisture. Cured sealants containing the copolymer-polysiloxane have high elongation properties.
Curable polyorganosiloxane, also known as silicone compositions have been used as sealants, caulks, adhesives, and in other similar applications because of their excellent water repellency, good adhesion, chemical and biological inertness, and good weather resistance. Such compositions generally contain a reactive polyorganosiloxane, crosslinking agents, and crosslinking catalysts. Polyorganosiloxane compositions are, however, relatively expensive and do not always provide satisfactory physical properties such as toughness and strength. In order to improve the physical properties of polyorganosiloxane compositions, various inorganic filler materials such as silica, diatomaceous earth, calcium carbonate, iron oxide and the like have been added. The use of such additives, however, has often resulted in an undesirably high viscosity which adversely affects the ease of application of the composition. In order to reduce the viscosity of filled polyorganosiloxane compositions to an acceptable level, organic solvents or non-reactive organosiloxanes can be used. However, this can result in undesirable shrinkage, or the release of environmentally undesirable organic components into the atmosphere or staining problems due to the non-reactive siloxane extrudate.
U.S. Pat. No. 4,138,387 to Bluestein relates to a polyolefin filled-organo polysiloxane composition which are allegedly stable dispersions comprised of a continuous phase of essentially ungrafted organo polysiloxane and a discontinuous phase of finely divided solid particles of a homopolymer or copolymer prepared from an organic monomer or monomers. The composition, however, is generally unacceptable as a sealant inasmuch as it has low elongation such as a maximum of only about 190 percent.
Curable dispersed copolymer-polysiloxane compositions are prepared by the in situ free radical polymerization in a polysiloxane fluid of at least two different classes of monomers, e.g. a first class of monomers which are capable of forming a polymer having a low Tg and a second class of monomers which are capable of forming a polymer having a high Tg. The copolymer, which can be either a thermoplastic or a thermoset, is generally a dispersed phase in the form of particles, the surface thereof generally having substantially high Tg polymers. The use of small amounts of a thixotrope renders the dispersed copolymer polysiloxane composition non-slump. The composition is generally viscous and is moisture curable. Utilization of the two different classes of monomers yields synergistic results upon cure in that the dispersed copolymer-polysiloxane composition has very high elongation as well as a 100% modulus of less than 50 psi. The composition also exhibits good flexibility and excellent weathering. Unlike previous reinforcing filler technology, the in situ polymerized particles have the unique characteristics of both reinforcing (strengthening) as well as plasticizing (increasing elasticity) the cured silicone network. Another attribute of the composition of the present invention is that they have good viscosity aging resistance before cure. Accordingly, the composition is suitable for use as a binder in caulks and sealants.
The dispersed copolymer-polysiloxane compositions of the present invention are generally made by reacting two or more different monomers in the presence of a polysiloxane fluid. The polysiloxane fluid generally contain a total of two or more reactive functional groups on the polymer chain, preferably at the terminal portion thereof.
The polysiloxane fluid desirably is an organo polysiloxane of the formula 
where R1 and R2, independently, is an alkyl having from 1 to 8 carbon atoms, desirably from 1 to 4 carbon atoms with methyl being preferred, or is an aromatic group or substituted aromatic group having from 6 to 10 carbon atoms with phenyl being preferred, and xe2x80x9cnxe2x80x9d is such that the weight average molecular weight of the polysiloxane is from about 2,000 to about 200,000 and desirably from about 15,000 to about 80,000 grams/mole. It is to be understood that the above polymers also contain, as noted above, two or more reactive functional groups (X) therein. The functional groups, independently, can be OH, or OR3, or N(R4)2, or 
or an 
group, where R3 through R12, are, independently, an alkyl having from about 1 to about 8 carbon atoms. The amount of the functional groups, i.e. m, is 1, 2, or 3. The one or more R groups, independently, is an alkyl having from 1 to 8 carbon atoms or an aromatic or an alkyl-aromatic having from 6 to 20 carbon atoms and optionally containing one or more functional groups thereon such as amine, hydroxyl, etc. A polysiloxane fluid can furthermore contain a blend of two or more different polysiloxanes and/or polysiloxanes having different viscosities. The polysiloxanes are generally a viscous liquid and are commercially available, e.g. Masil(copyright) SFR 6,000 from PPG Corporation and Wacker 6LV from Wacker Corporation.
The organopolysiloxane fluid generally constitutes a reactive continuous phase containing a discontinuous phase therein which comprises copolymer particles made in situ by free radical polymerization. Desirably, two or more, and preferably two types of monomers are utilized wherein one, if homopolymerized, forms a low Tg polymer and the other, if homopolymerized, forms a high Tg polymer. As noted above, the copolymer can either be a thermoplastic, or if crosslinked, a thermoset.
The one or more monomers utilized which otherwise would form a polymer having a low Tg, i.e. generally from about xe2x88x9270xc2x0 C. to about 0xc2x0 C. and desirably from about xe2x88x9255xc2x0 C. to about xe2x88x9210xc2x0 C., include the various alkyl acrylates, and the like. The alkyl acrylate monomers generally have an alkyl portion which contains from 1 to 18 carbon atoms, and desirably from 1 to 8 carbon atoms. Examples of such suitable acrylates include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, 1-ethyl propyl acrylate, 1-methyl pentyl acrylate, pentyl acrylate, hexyl acrylate, 2-ethylhexly acrylate, and the like, with n-butyl acrylate being highly preferred. A small amount of approximately 20 percent or less and desirably from about 2 to 8 percent by weight of the various alkyl acrylates can contain functional groups thereon. Such groups include hydroxyl, epoxy, acetoacetyl, acrylamide, and the like, are preferably terminal groups and serve to improve adhesion to various substrates such as metals, concrete, wood, etc.
One or more monomers are also utilized which otherwise would form a polymer having a high Tg, i.e. generally from about 1xc2x0 C. or 5xc2x0 C. to about 150xc2x0 C. and desirably from about 20xc2x0 C. to about 120xc2x0 C. Such monomers include vinyl esters, acrylonitrile or derivatives thereof, vinyl substitute aromatics, alkyl methacrylates, vinyl chloride, vinylidene chloride, and the like. The non-vinyl portion of the vinyl ester generally contains a total of from 2 to about 10 carbon atoms, desirably from about 2 to about 8 carbon atoms with acetate, i.e. vinyl acetate, being highly preferred. With respect to the acrylonitrile monomers, while the same is generally utilized, alkyl derivatives thereof containing from 1 to about 6 carbon atoms such as methyl acrylonitrile, ethyl acrylonitrile, etc. can also be utilized. The vinyl substituted aromatics generally contain from 8 to about 12 carbon atoms and specific examples include styrene, alpha-methyl styrene, vinyl toluene, and the like. The alkyl methacrylates include monomers wherein the alkyl group contains from 1 to 18 carbon atoms, and desirably from 1 to 8 carbon atoms. Specific examples include methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, ethyl hexyl methacrylate and the like, with methyl methacrylate, being preferred. Of the various one or more monomers which are capable of forming a polymer having a high Tg, the vinyl esters are preferred, such as vinyl acetate inasmuch as it has a reactive ratio with the various acrylate monomers such that a large portion of the vinyl acetate monomers polymerize after the various acrylate monomers have polymerized.
The copolymer particles are generally formed by polymerization at the same time, for example, simultaneously, the low Tg polymer forming monomers and the high Tg polymer forming monomers in the presence of the organopolysiloxane fluid. The type of copolymer will generally depend upon the reactivity ratios of the particular monomers. Reactivity ratios are defined in the Polymer Handbook, second edition, by J. Brandrup and E. H. Immergut, editors, 1975. If the amount and reactivity ratios of the monomers is decidedly different, the copolymers formed will initially be rich in the more reactive monomer until the more reactive monomer is consumed. Then the resulting copolymer portion formed will subsequently or terminally be rich in the less reactive monomer. If the reactivity ratios are similar, a random copolymer will generally be formed. Moreover, if the high Tg polymer forming monomer has a reactivity ratio similar to that of the low Tg polymer forming monomer, it is then desirable to add a large portion of the high Tg polymer forming monomer in a second or subsequent stage so that the copolymer particles be surface rich in the high Tg polymer. During the formation of the copolymers, small amounts of low Tg homopolymer and of high Tg homopolymer will also be formed. The weight of high Tg polymer forming monomers can vary from about 2.5 percent to about 50 percent and desirably from about 20 percent to about 40 percent by weight (based upon the total weight of monomers, i.e. high and low forming the copolymer particles).
Although a majority of the repeat units in the copolymer will be derived from low Tg monomers, desirably the copolymer particles have a majority or are phase rich on the surface thereof with repeat units in the copolymer and/or homopolymers derived from high Tg monomers. One manner of forming such particles is to add a significant amount such as from about 50 to about 100 percent by weight (i.e. from about one-half to all) of high Tg forming monomers during a late stage or a second stage of the polymerization. By late stage or second stage polymerization it is meant that some or most of the high Tg forming monomers are added after a certain or specified amount, for example, at least about 60 percent, desirably at least about 70 percent, and preferably at least about 80 percent of the previously added monomers (e.g. mostly low Tg forming monomers) have been polymerized.
Regardless of the monomer weight ratio, it is generally thought that the surface composition of the dispersed thermoplastic copolymer particles, have a high Tg, e.g. greater than about 5xc2x0 C. and preferably greater than about 20xc2x0 C. Otherwise viscosity aging sensitivity would often render the polysiloxane composition generally unsuitable for non-slump sealant applications. Whether the surface Tg of the copolymer particles have a desired high Tg can be determined by the use of various methods or apparatus such as by atomic force microscopy, through the use of solid state nuclear magnetic resonance or through ESCA, i.e. electron spectroscopy for chemical analysis.
Moreover, it has also been found that the interior of the dispersed copolymer particles should not exceed a Tg of zero degrees centigrade and desirably not above minus 10xc2x0 C. Thus, the dispersed phase contains copolymer particles predominantly having high Tg polymers on the surface thereof and low Tg polymers in the interior thereof. The surface of the particles need not contain solely the high Tg polymer thereon and the same may exist as a partial coating, as particles, aggregates, etc., thereon, and the like. Moreover, the dispersed phase will at times contain small amounts of the organopolysiloxane or grafted polyorganosiloxane therein. Conversely, the continuous organopolysiloxane phase can contain some high and/or low Tg polymer-grafted polysiloxanes therein.
The shape of the dispersed copolymer particles can vary but generally is spherical or nearly spherical with the size thereof ranging from about 5 or 10 microns up to about 50, 30, or 20 microns in diameter. The size distribution of the dispersed particles is usually not monodisperse.
The weight percent of the discontinuous phase, i.e. the phase containing substantially copolymers, e.g. copolymers derived from one or more high Tg forming monomers, and one or more low Tg forming monomers is from about 10 or 20 to about 85 percent and preferably from about 50 to about 75 percent by weight based upon the total weight of the discontinuous phase and the continuous polysiloxane phase.
The utilization of the dispersed copolymer particles having a surface Tg of at least 5xc2x0 C. and preferably at least 20xc2x0 C. and a lower Tg interior in a polysiloxane fluid unexpectedly yields a composition which has good viscosity aging resistant properties. That is, upon standing at ambient temperature, the viscosity increase of the dispersed copolymer-polysiloxane composition before cure is little or small. Thus, the compositions do not have a viscosity increase such that they become an elastic material. Suitable viscosity aging properties include an increase of viscosity of generally less than 100%, desirably less than 50%, and preferably less than 25%, after aging for 24 hours at ambient temperature, i.e. 20xc2x0 C., in accordance with ASTM D2452-75.
The dispersed copolymer-polysiloxane composition of the present invention also has unexpectedly been found upon cure to yield high elongations at break, such as at least 300 percent or 400 percent, desirably at least 500 or 600 percent, and preferably at least 700 or 800 percent up to about 1,100 percent at 20xc2x0 C. Moreover, the 100% tensile strength modulus is from about 10 to about 50 psi.
The copolymer forming monomers are polymerized in the presence of a free radical initiator. Desirably, various initiators are utilized which are soluble in the monomers such as azo and desirably organic peroxide initiators. Examples of suitable organic peroxides include benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, dialkyl peroxides such as di-tertiary-butyl peroxide and dicumyl peroxide; hydroperoxide and decylene hydroperoxide; cyclic peroxides such as 1,5-dimethylhexane-1,5-peroxide; peresters such tert-butylperbenzoate, tert-butyl-peroxy isopropyl carbonate, tert-butylperoctyate and tert-butylperacetate. Examples of azo compounds include azobisisobutyronitrile, 2,2-azobis-2,4-dimethylvaleronitrile, 2-carbamoyl, azoisobutylonitrile, dimethyl-2,2xe2x80x2-azobisisobutylate and 1,1-azobiscyclohexane carbonitrile. Generally, various persulfates are not utilized inasmuch as they are aqueous catalysts and are not soluble in the copolymer forming monomers of the present invention. The amount of the initiators is generally from about 0.05 to about 5.0 parts by weight for every 100 parts by weight of all of the low Tg and high Tg polymer forming monomers.
The polymerization temperature will vary depending upon the particular monomers utilized, but generally is from about 60xc2x0 C. to about 130xc2x0 C. and preferably from about 70xc2x0 C. to about 100xc2x0 C. in order to insure a quick reaction.
The actual in situ polymerization of the copolymer can proceed in any desired manner. A preferred mode of polymerization involves adding an organo polysiloxane to a reaction vessel which is free of oxygen, e.g. a nitrogen atmosphere. A mixture of the two or more monomers with at least one monomer capable of forming a low Tg polymer and a different monomer capable of forming a high Tg polymer, as well as initiators, are metered into the reaction system which has previously been heated to the polymerization temperature. Polymerization then occurs with the contents of the reaction vessel being mixed utilizing any conventional mixing device so that the formed copolymer particles are dispersed as a separate phase within the polysiloxane which exists generally as a continuous phase. Polymerization as well as the addition of monomers thereto is continued until a suitable amount of dispersed copolymer particles have been formed.
Optionally, one or more crosslinking compounds having more than one polymerizable unsaturated olefinic groups such as divinyl benzene, allylmethacrylate, and the like, in amounts of up to 5 parts by weight, desirably from about 0.1 to 2 parts by weight, and preferably from about 0.1 to 0.5 parts by weight for every 100 parts by weight of the copolymer forming monomers can be used, provided that severely agglomerated or irregularly shaped particles are not formed in amounts sufficient to render the dispersion too viscous or unstable.
Another important aspect of the present invention is the utilization of low amounts of a thixotropic agent such as generally less than 3 parts by weight, desirably from about 0.05 to about 2 parts by weight, and preferably from about 0.05 to about 0.5 parts by weight per 100 parts by weight of the dispersed copolymer-polysiloxane composition. Examples of suitable thixotropic agents include hydrogenated castor oil, fumed silica, precipitated calcium carbonate, and the like. The above-noted amounts of thixotropic agents result in a non-slump composition, i.e. non-sagging in vertical joints as measured by ASTM D 2202-938.
The dispersed copolymer-polysiloxane compositions of the present invention, are cured by generally subjecting them to moisture. Either a conventional one-component or two-component cure system can be utilized. In a conventional one-component cure, the polysiloxane is converted to a compound having an alkoxy, an oxime, an enoxy, an amido, an amino, or an acetoxy blocking group in a manner well known to the art and to the literature. Conventional condensation catalysts are utilized such as an organo tin, for example, dibutyltin diacetate, dibutyltin dilaurate, or dimethylhydroxytin oleate, or an organo titanate. Optionally, the blocked one-component cure system can contain crosslinking agents as set forth herein below. In a two-component cure system, crosslinking agents such as a multi-functional alkoxy silane or oligomers thereof and catalysts are kept separate from the polysiloxane until reaction. The amount of catalyst for the two component system, is generally much higher than in the one component system. Such cure systems are well known to the art, e.g. see Rubber Technology, 3rd Edition, pp. 406-07, 1987, by Maurice Morton, Van Nostrand Reinhold, which is hereby fully incorporated by reference.
While a variety of conventional crosslinkers are suitable, oxime crosslinkers are preferred, such as for example, vinyl tris-methylethylketoximosilane, and methyltris-methylethylketoximosilane. Methyltris-methylethylketoximosilane (MOS) is available under the trade name OS-1000 from Allied Signal Corp. Other crosslinkers are also suitable; such as for example, alkoxysilanes, epoxyalkylalkoxysilanes, amido silanes, aminosilanes, enoxysilanes and the like, such as tetraethoxysilanes, methyltrimethoxy silane, vinyl trimethoxysilane, glycidoxypropyltrimethoxsilane, vinyl tris-isopropenoxysilane,methyl tris-isopropenoxysilane, methyl tris-cyclohexylaminosilane, and methyl tris-secondarybutylaminosilane. Mixtures of crosslinkers can also be employed. The amount of the crosslinking agent is generally from about 0.2 to about 20 parts by weight, desirably from about 1 to about 10 parts by weight, and preferably from about 1.5 to about 6.5 parts by weight for every 100 parts by weight of said copolymer-polysiloxane.
Another important aspect of the present invention is that various compatibilizing agents are optionally utilized to generally form a thin layer which compatibilizes the generally otherwise incompatible polysiloxane with a dispersed high Tg-low Tg polymer phase and thus helps control the particle size, improve tensile strength properties, and result in lower dispersion viscosities. Suitable compatibilizing agents include vinyl containing or mercapto containing polyorganosiloxanes, or macromonomers such as monomethacryloxypropyl terminated polydimethylsiloxane, and the like, with vinyl terminated polydimethyl siloxane such as PS443 from United Chemical Technologies, Inc. being preferred. The amount of the optional compatibilizing agents are generally up to about 15 parts by weight, and desirably from about 1 to about 5 parts by weight for every 100 parts by weight of the high and low Tg polymer forming monomers.
The dispersed copolymer-polysiloxane composition generally has a low viscosity which permits it to be readily extruded. Thus, the copolymer-polysiloxane can be used in low temperature applications. Upon exposure to moisture, the composition cures and forms a low temperature flexible, water repellant, thermal oxidative resistant, UV resistant material. The composition also upon cure has low shrinkage and is soft and pliable. Unexpectedly, the dispersed copolymer-polysiloxane composition has synergistic elongation properties at break as noted above of from about 300 to about 1,100 percent and yet has low 100% tensile modulus properties, the combination of which is highly desired for sealant properties. These properties were unexpected inasmuch as polysiloxane compositions made from only low Tg forming monomer(s) or from only high Tg forming monomer(s) such as those contained in conventional silicone sealants generally had low elongations, typically less than 300 percent.
Sealant
Sealant compositions which are particularly useful as caulks, are comprised of the dispersed copolymer-polysiloxane, one or more of the above noted crosslinkers, and optionally though preferably: an adhesion promoter; a reinforcing agent; a chain extender; and a plasticizer. The sealants in their uncured states have little sag, generally less than about 1.0 inches, desirably less than about 0.5 inches, preferably less than about 0.2 inches, most preferably about 0. The uncured sealants are easy to tool and have a tooling life of from about 5 to about 240, desirably from about 10 to about 180, and preferably from about 20 to about 150 minutes. Once the sealant cure is initiated, the sealants become tack free in generally about 0.5 to about 12 hours, desirably from about 1 to about 8 hours, and preferably from about 1.5 to about 7 hours. The sealants become substantially cured, i.e. chemically crosslinked, in about 7 days although this may vary depending upon the curing system, particularly the catalyst employed. The sealants are typically completely cured at about 21 days at 25xc2x0 C. and 50% relative humidity.
The cured sealant has a shore A hardness generally from about 3 to about 45, desirably from about 8 to about 35, and preferably from about 10 to about 25; a tensile strength generally from about 20 to about 400, desirably from about 50 to about 300, and preferably from about 60 to about 200 psi; an elongation to break of generally from about 250 to about 1600, desirably from about 350 to about 1400, and preferably from about 400 to about 1200 percent; and a 100% extension modulus of generally from about 8 to about 130 psi, desirably from about 10 to about 100 psi, preferably from about 10 to about 50 psi, and most preferably from about 15 to about 35 psi. The extension modulus is measured according to ASTM D412 at 100% elongation.
The amount of the adhesion promoter in the sealing composition is generally from 0 to about 15, desirably from about 0.3 to about 15, preferably from about 0.75 to about 6, and more preferably from about 1 to about 3 parts by weight based upon 100 parts by weight of the copolymer and polysiloxane. The amount of the reinforcing agent is generally from 0 to about 100, desirably from about 0.1 to about 100, preferably from about 0.1 to about 60, and more preferably from about 0.2 to about 30 parts by weight based upon 100 parts by weight of the copolymer and the polysiloxane. The amount of the plasticizer is from 0 to about 80, desirably from about 5 to about 80, and preferably from about 10 to about 30 parts by weight based upon 100 parts by weight of the copolymer and the polysiloxane. The amount of the chain extender is generally from 0 to about 12, desirably from about 0.2 to about 12, preferably from about 0.2 to about 8, and more preferably from about 0.5 to about 5 parts by weight based upon 100 parts weight of the polysiloxane.
The plasticizer contributes to the flexibility, particularly low temperature flexibility, of the cured sealant. Unexpectedly, the addition of the plasticizer unlike conventional polysiloxanes which result in reduced tensile strength, imparts improved tensile strength to the copolymer-polysiloxane admixture. The plasticizer also modifies the modulus of the cured sealant; if modulus values exceed about 100 psi at 100% extension, the cured sealant tends to pull the surface of the material, particularly materials like concrete, to which the sealant is applied. The modulus values of the cured sealant are preferably less than about 60 psi, more preferably less than about 40 psi.
The plasticizer generally has a number average molecular weight of from about 100 to about 800 and desirably from about 200 to about 400. Preferably the plasticizer has a boiling point greater than about 100xc2x0 C., at 1 atmospheric pressure. Suitable plasticizers are phthalate esters, dibenezoate esters, phosphate esters, and adipate esters. Examples of phthalate esters are dibutyl phthalate, dioctyl phthalate, dimethyl phthalate, diisodecyl phthalate, butyl benzyl phthalate, texanol benzyl phthalate, C7 benzyl phthalate, and C9 benzyl phthalate. Examples of dibenzoate esters are dipropylene glycol dibenzoate, polypropylene gylcol dibenzoate, diethylene glycol, and triethylene glycol dibenzoate. Examples of adipate esters are dioctyl adipate, ditridecyl adipate, and dialkyl adipate. Examples of phosphate esters are tricryesyl phosphate, trioctyl phosphate, triphenyl phosphate, and t-butylphenyl diphenyl phosphate. Other suitable plasticizers are for example terephthalates such as 1,4-benzenedicarboxylates, and trimelliatics such as 1,2,4-benzenedicarboxylates;. A suitable butyl benzyl phthalate, a phthalate ester of butyl alcohol and benzyl alcohol, is commercially available as Santicizer 160 formerly from Monsanto Solution Company, St. Louis, Mo., now Solutia St. Louis, Mo.
The chain extenders are difunctional molecules which extend the length of the polysiloxane polymer chains and modify the modulus of elongation of the cured sealant. Suitable classes of chain extenders are silane chain extenders such as amino silanes, amido silanes, acetoxy silanes, and aminoxy silanes. Suitable chain extenders are for example, methylvinyl bis-N,-methylacetamidosilane, methylhydrogendiacetoxysilane, dimethylbis-diethylhydroxylaminosilane and dimethylbis-secondarybutylaminosilane. Dimethylbis-secondary butylaminosilane is available under the trade name SB-72 from Wacker Silicones of Adrian, Mich.
The adhesion promoter, although optional, is highly preferred; the adhesion promoter provides the sealant with long term adhesion to the substrate. Suitable classes of adhesion promoters are aminoalkyl, mercaptoalkyl, epoxyalkyl, ureidoalkyl, carboxy, acrylate and isocyanurate functional silanes. Examples of suitable adhesion promoters are mercaptopropyltrimethoxysilane, glycidoxpropyltrimethoxysilane, aminopropyltriethoxysilane, aminoethylaminopropyltrimethoxysilane, ureidopropyltrimethyloxysilane, bis-xcex3-trimethoxysilyl-propylurea, 1,3,5-tris-xcex3-trimethoxysilylpropylisocyanurate, bis-xcex3-trimethoxysilylpropylmaleate and fumarate and xcex3-methacryloxypropyltrimethoxysilane A suitable silane adhesion promoter is aminopropyltriethoxysilane which is available under the trade designation A-1100 Silane from OSi, a division of Witco Corporation.
The reinforcing agents are optional although highly preferred, particularly when the sealant is used as a caulk. Reinforcing agents increase tensile strength in the cured sealant and reduce sag of the uncured sealant. The reinforcing agent also functions as a thixotrope. Such reinforcing agents are finely divided particulates and include both the conventionally known reinforcing agents and semi-reinforcing agents, typically having a particle size less than about 10 microns, preferably about 5 microns or less, more preferably about 0.1 microns or less. Suitable reinforcing agents include hydrophobic treated fumed silicas, such as TS 720 from Cabot Corporation, or R-972 from Degussa Corporation, hydrophobic precipitated calcium carbonates, talc, zinc oxides, and polyvinyl chloride powders. Other ingredients can also be utilized in the sealant formulation in amounts up to about 20 parts by weight and desirably from about 0.01 to about 15 parts by weight per 100 parts by weight of the copolymer and the polysiloxane. Such ingredients include fungicides. Moreover, extender fillers such as ground calcium carbonates and diatomaceous earth are optionally employed. Such extenders have minimal or no reinforcing effect and/or minimal or no thixotropic effect.
UV stabilizers can be optionally added. Pigments or colorants such as titanium dioxide, iron oxide, carbon black are optionally employed to impart color to the sealant and/or to act as ultraviolet stabilizer. LTV inhibitors, anitozonates are also optionally added.
The sealant in its uncured state may optionally contain solvents such as organic solvents to reduce the viscosity; such solvents are employed where the sealant is to be used as a coating such as for a roof. Such solvents are less preferred where the sealant is to be used as a caulk since as such solvents evaporate, the cured sealant shrinks which is not desirable.
The present invention relates to a family of silicone sealants which generally meet all of the performance features demanded by the construction industry for joint and general sealing such as; non-staining characteristics on porous substrates like white marble, virtually no change of properties during weather exposure, low modulus elastomeric behavior to accommodate joint movement without adhesive or cohesive failure, extended tooling life which allows a worker to apply the sealant in long joints before having to tool the surface of the sealant and primerless adhesion to a broad spectrum of substrates such as anodized aluminum, concrete, brick, mortar, marble, granite, limestone, porcelain, glass, painted surfaces, wood, PVC, polyacrylate, polycarbonate, and polystyrene, etc.
Unlike conventional silicone sealants wherein the tooling time generally ranges from about 2 to about 30 minutes and even less at elevated temperatures and humidities, for example, from about 1 to about 10 minutes, the copolymer-silicone sealants of the present invention can generally have tooling times in excess of 2 hours. As noted above, the copolymer-silicone sealant compositions of the present invention have good low modulus characteristics such as low as 10 to 20 PSI at 100 percent extension. Conventional silicone sealants generally do not have such a high elongation with extreme low modulus and can fail on weak tensile stress surfaces such as concrete.
With proper compounding, the copolymer-polysiloxane compositions of the present invention can also be used to coat fabrics, or to form gaskets. Another large area of utility is as silicone alloys, including thermoset alloys such as RTV (room temperature vulcanizable) silicone-acrylate alloys, molded silicone rubbers, and silicone-acrylate epoxy additives wherein the silicone can be the copolymer-polysiloxane composition of the present invention or it can be a mixture or blend of a conventional silicone and the copolymer-polysiloxane composition of the present invention. The composition of the present invention can also be used in medical applications, electronic applications, automotive applications, textile applications, paper coatings, polishes, cosmetic applications, pharmaceutical applications and as processing aids.